1. Field of the Invention
The present invention relates to a method for manufacturing carbon nanotubes, and more particularly, to a method for manufacturing carbon nanotubes by binding carbon nanoparticles manufactured by a conventional method.
2. Description of the Related Art
Conventionally, carbon nanotubes have been manufactured by a physical method, such as arc discharging or laser vaporization, or by a chemical method such as chemical vapor deposition (CVD).
FIG. 1 shows an arc discharging apparatus applied to the conventional arc discharging method. Initially, graphite rods are mounted as a cathode 11 and an anode 13, and a voltage is applied across the two electrodes to occur discharging between the two electrodes. As a result, carbon particles falling away from the anode graphite rod are attached to the cathode graphite node whose temperature is maintained to a low level, by attraction.
FIG. 2 shows a laser vaporization apparatus applied to the conventional laser vaporization method. Initially, the temperature of a reactor 27 is maintained at about 1200, and a graphite 23 placed in the reactor 17 is irradiated by a laser beam 21 to vaporize the graphite 23. The graphite vapor is adsorbed onto a collector 25 maintained at a low temperature.
In the conventional physical methods for manufacturing carbon nanotubes, such as arc discharging or laser vaporization, a pure anode graphite rod having a cavity filled with metal powder, such as Co, Ni, Fe, or Y, is used to obtain single-walled or multiple-walled carbon nanotubes. However, forming the graphite node containing a predetermined amount of a particular catalytic metal complicates the overall carbon nanotube manufacturing process, and thus the physical methods cannot be applied to produce carbon nanotubes on an industrial scale. In addition, single-walled carbon nanotubes produced by the physical methods contain a great amount of impurities, such as amorphous carbon or metal particles, and thus needs an additional purification process.
FIG. 3 shows an apparatus applied to a conventional plasma enhanced chemical vapor deposition (PECVD) method. According to the PECVD method, a reactive gas is discharged in a vacuum chamber by a direct current or high-frequency electric field applied across two electrodes. Referring to FIG. 3, a substrate 31 on which carbon nanotubes are to be grown is placed on a grounded lower electrode 32, and a reactive gas is supplied between an upper electrode 34 and the lower electrode 32. A thermal resistive heater 33 is mounted underneath the lower electrode 32, or a filament 35 is disposed between the upper electrode 34 and the lower electrode 32, to decompose the reactive gas. The energy needed to decompose the reactive gas and to synthesize the carbon nantotubes is supplied from a high-frequency power source 37. As the reactive gas, CH4, C2H2, H2, etc. are used.
Compared with the physical methods described above, the conventional CVD method is favorable for mass production and advantageously does not need an additional purification process. However, similar to the conventional physical method, it is not easy to inject and control a catalyst. In addition, the conventional CVD method needs a high-temperature growing process and thus increases the complexity of the process, energy consumption, and costs.